1. Field
Embodiments of the present invention relate to antenna arrays.
2. Related art
Dual polarity flared notch antennas arrays are commonly used, for example, in radar systems. For some applications, it is desirable for the two polarities of the dual polarity flared notch antenna array to have coincident phase centers.
FIG. 1A is a cross sectional view of a conventional flared notch antenna 100 having two flares 110, a feed 120 crossing a notch 130 located between the two flares 110 and backed by a cavity 140. Due to the location of the feed 120 across the notch 130, a conventional flared notch antenna 100 cannot be operated in a dual polarity arrangement with coincident phase centers because the flares 110 and the feed 120 of the second polarity would interfere (e.g., intersect or cross) with those of the first polarity.
FIG. 1B is a cross sectional view illustrating a conventional flared notch antenna 100′ having an alternative feed scheme including an alternative feed 120′.
FIGS. 2A and 2B are cross sectional views of alternative flared notch antennas which can be used to provide a coincident phased dual polarity flared notch antenna array. FIG. 2A is reproduced from FIG. 2 of W. R. Pickles, et al. “Coincident Phase Center Ultra Wideband Array of Dual Polarized Flared Notch Elements” Antennas and Propagation Society International Symposium, IEEE 2007. In the antenna arrays shown in FIGS. 2A and 2B, the feed 220 is split into a first and a second feed 222 and 224. Similarly, the notch 230 is split into first and second slots 232 and 234 which are backed by their respective cavities 242 and 244. The first and second feeds 222 and 224 extend across their respective slots 232 and 234. Because the feed 220 no longer crosses the center of the structure (e.g., in the middle of the space between the flares 210), this structure makes it possible to arrange flares and feeds for both the first and second polarities without the use of an offset in the z-direction.
In addition to a balun, an impedance transformer is generally used as part of a radiating element in order to provide impedance matching between the source impedance (generally, 50Ω) and the free space impedance (approximately 377Ω). In the conventional flared notch radiator 100 illustrated in FIG. 1A, the flares 110 are used as the impedance transformer to provide this impedance matching. However, because the flares 110 are directly connected to the feed 120, the flares must provide all of the matching from 50Ω to 377Ω and therefore are relatively long.